1. Field of the Invention
The invention concerns a method and device for mapping radiation sources, to make it possible to locate such sources in a three-dimensional environment which may be known or unknown at the start.
2. Discussion of the Background
The idea of detecting radiation sources such as radioactive leaks by comparing an image of these sources, taken by a specialised item of equipment, and a visual or video image of the environment taken by an ordinary light-sensitive camera has already been applied. The use of the images can be effected empirically by the user, finding the locations of the radioactive sources on the visual image; in a rudimentary design of the method, he identifies the elements of the environment, restored on the visual image, which correspond to the places on the image of the sources on which a source has been recorded. The identification of the position of the sources is however not very precise and calls on the judgement and knowledge of the user with regard to the environment: he may thus know in advance the places in the environment where a leakage is liable to occur and identify them easily when it arises. Though such a method is sufficient in certain situations, it does not lend itself to automatic processing, notably if repair work is to be entrusted to a robot, which must know precisely the position of the source in three-dimensional space in order to reach it.
In a more improved method which is described in French patent No 2 652 909, a camera is used which is combined with obturators and means of converting the radioactive radiation, which enables it to record in turn a visual image and a radioactive emission image of the environment. The two images are supplied to automatic processing means, which superimpose them, which gives, without error, the position of the sources in the field of the camera. However, as this work is carried out on a two-dimensional image, the problem mentioned above is not resolved: an automatic use system cannot determine the distance of the source, and if it is indeed at the position of a detail of the environment on which it is superimposed, or if it is situated in front of or behind it on the radius of sight of the camera.
In addition, tomography methods are known which make it possible to know the positions of radioactive sources in a three-dimensional environment; the cameras (or, more generally, the means of taking two-dimensional images) are moved around the object and the information read on the images is combined in order to derive therefrom the position of the sources. This amounts to inverting, directly or indirectly, a system of equations expressing the fact that the radiation received by each image point is the sum of the radiation emitted along the line of projection or sight of the camera which ends at this point. However, it is necessary to know the position of the camera each time an image is taken, which is not always possible in the situations envisaged here, since the robots are not always sufficiently precise, nor even provided with position coders which indicate where they have arrived.
Finally, it is necessary to cite the international patent application WO 96/20421, which describes a double method of tomography and superimposition of two three-dimensional images thus obtained, where one illustrates the visible details of the object examined and the other depicts a view of the object by X-ray or the like. However, the two images are calculated in the same way and separately (except in order to apply correction calculations for the effects of the distortion, enlargement, etc produced by each of the photographic means); they are put in a relationship of equality and have the same importance.
This patent therefore does not give the idea of using a visual image of the environment in order to assist in determining the positions of point radiation sources in this environment, without it being necessary to have recourse to the conditions of obtaining tomographic images.
The object of the invention is therefore to make it possible to completely and precisely locate radiation sources, radioactive or others, in a three-dimensional environment.
The essential idea of the invention is that a three-dimensional model of the environment is used, established in advance by taking visual images, on which there are placed the sources registered on other images, which are correlated with the visual images.
The purpose of the model is therefore not only to provide a graphical representation of the positions of the sources in the environment, but particularly to help to determine these positions.
In its most general form, the invention thus concerns a method for the three-dimensional mapping of sources of radiation in an environment, comprising a first taking of a visual image of the environment and a first taking of an image of the sources, characterised in that it comprises a second taking of a visual image of the environment and a second taking of an image of the sources; an establishment of a visual three-dimensional model of the environment by searching for and identification of analogous elements of the visual image and then by location calculations for the homologous elements of the visual images; a location in the model of the environment of projection lines leading from the sources to the images of the sources; and calculations of positions of points of intersection of the projection lines in the model.
A device for implementing this method comprises a device for taking images of the radiation, a pair of means of taking visual images of an environment of the radiation sources, the means of taking visual images being oriented in directions such that they have all or part of their field of vision in common and mounted on a rigid common support which is non-deformable but adjustable with the means of taking images of the radiation, and photogrammetry means able to reconstitute a visual three-dimensional model of the environment from the visual images and to superimpose a three-dimensional model of the radiation sources using images of the radiation on the visual model.